Modern agriculture is determined by high pressure of competition which is further intensified by the increasing globalization. In particular in dairy farming great value is therefore placed on high profitability in the production of milk. For this purpose, however, it is particularly important to aim at a certain degree of automation in the production of milk and therefore allow attending to a huge stock of animals with a not excessively large amount of staff. Furthermore, the quality of the gained milk must have a high standard and it is also essential that the respective national and international regulations regarding the quality of the milk are carefully observed. A very important aspect of achieving a permanently high yield of milk is to be seen in keeping the health of the animals in a herd at a high level, so that, in the long run, the highest possible yield of milk can be obtained from every single animal.
During increasing automation in attending to a great number of milk animals certain milking methods have become accepted in the past, which, on the one hand, aim at allowing to attend to and therefore also milk a great number of animals with a small amount of staff being required and, on the other hand, provide surroundings for the animals which are as optimal as possible to ensure the health of the animals in the log run. For this purpose, so-called milking robots are used in many large agricultural farms where, for example, the milking process is almost fully automated, so that normally more than two milking processes per day can be accomplished on one individual animal, the number of persons required being low. On other farms, a semi-automatic milking strategy is applied, which involves the use of so-called milking parlours where certain activities are carried out or at least supervised by the staff, and merely the milking process itself is almost fully automated.
Depending on the process strategy, the milking process itself is normally carried out such that after a certain stimulation phase a negative pressure is generated at the respective teat, so that milk flow occurs, with a massage action interrupting the milking flow at regular intervals being typically carried out. To this end, pressure from outside is applied to the teat at regular intervals, so that a certain backward flow of blood and lymph takes place during this phase and also appropriate pressure conditions are generated at the teat, which at least roughly imitate the natural sucking behaviour of a calf. The milking function and, in part or completely, the function of stimulation before, during and after the actual milking process are executed in a controlled manner with the aid of a milking equipment, which has respective teat cups, with the support of a qualified person or completely automatically. The individual teat cups are normally implemented as rigid cups backed on the inner side with an elastic material, the so-called teat rubber. Hence, the teat rubber is in direct contact with the teat of the animal and thus, in a certain way, represents an “interface” between animal and machine. Therefore, the teat rubber must have a plurality of properties to comply with the requirements occurring in automated milking, viz. the teat rubber must first of all allow appropriate pressure conditions to be obtained under the teat to start the desired milk flow. Hence, the teat rubber must be adapted to be slipped on the teat on the one hand and, nevertheless, must generate a sufficiently high leak tightness at the teat bottom to thus allow the generation of the desired negative pressure.
Furthermore, in the desired periodic interruption of the milk flow and the resultant massage action, there must be a sufficiently high elasticity to ensure folding in or collapsing of the teat rubber below the teat. This is accomplished by applying (pressurized) air to the outside of the teat rubber. In this connection, frequencies of approximately 0.2 to 2 Hz are normally obtained, so that throughout its service life the respective material of the teat rubber is to accomplish a multitude of folding processes with almost equal behaviour. Furthermore, the teat rubber must, all in all, show a good cleaning behaviour, since nucleation must be suppressed to the highest possible degree, so that bacteria will be prevented from being transmitted from one animal to the other to a very large extent. Furthermore, the material must be as inert as possible from a chemical view-point, so that material will not be separated into the milk and, hence, the high standards in terms of hygiene and quality will be observed.
As a result of the many criteria to be met by a teat rubber, a plurality of material mixtures is presently in use; normally, appropriate polymer materials are employed in the production of teat rubbers. Therefore, the diverse materials can produce very different results with respect to durability, efficiency as regards high yield and particularly with respect to the health of the animals. In particular, with regard to the last-mentioned aspects, consistency and material properties proved to be important characteristics to increase the milking process efficiency. For instance, relatively soft materials, for example, silicone mixtures, are advantageous for a high yield and milk health, since a contact area that is comfortable for the animal or an “interface” between animal and machine in the milking process can be created in this way. Hence, respective mechanical strain as well as the resultant hardening and pathological change of the teat can be suppressed significantly in contrast to relatively hard rubber mixtures.
As a result of the many different requirements to be met by a teat rubber, teat rubbers in use must be exchanged relatively often, so that efficient production methods are required in which the teat rubbers are produced efficiently in great number and with constantly high quality. The teat rubbers are normally produced from a polymer material mixture under pressure and heat on the basis of an appropriate mould by means of an injection moulding process. In this manufacturing process, the corresponding material mixture is heated and thus assumes a viscous state and, under a relatively high pressure, the latter is injected into a corresponding mould where, after a certain curing time, a respective preform of the teat rubber is formed which is then removed from the mould and subjected in a suitable manner to a finishing treatment so as to obtain the final state of the teat rubber. To achieve an appropriately efficient production of the teat rubber, material mixtures are frequently used, which allow an efficient manufacturing process, particularly during the removal of the still hot preform. Normally, harder material mixtures allow a better handling, since they are of a higher mechanical stability. In the processing of material mixtures resulting in a relatively soft teat rubber, e.g. silicone teat rubbers, the removal of the teat rubber preform from respective components of the injection mould is a critical process, since an excessive mechanical strain or any other form of excessive deformation can result in an irreversible modification of the material of the preform and can thus make the teat rubber unusable. For allowing a wide range of different material mixtures and particularly soft mixtures of material, which can be advantageous in the use of the teat rubbers, to be efficiently processed in the production process, suitable measures are therefore required to avoid, as far as possible, irreversible modifications of the teat rubber material after the injection moulding and before the finishing treatment.